1. Technical Field
The present disclosure relates to a capped integrated device with protective cap, to a composite wafer incorporating integrated devices, and to a process for bonding integrated devices with respective protective caps.
2. Description of the Related Art
As is known, several integrated electronic devices, and, in particular, microelectromechanical devices, are provided with a cap that protects from dust and other contaminating agents, as well as from impact, both during the final machining steps and in use. For example, the introduction of dust is particularly harmful for microelectromechanical devices, which have microstructures and movable parts that are very brittle and can easily get damaged.
Normally, the devices are provided in arrays in semiconductor wafers, which are bonded to further protective wafers, which form the protective caps. Composite wafers are thus provided, which are then cut into dice, each of which comprises a portion of the semiconductor wafer, containing a device, and a portion of the protective wafer, forming a cap.
The protective wafers are frequently made of semiconductor material, but, in principle, they could also be made of some other material, such as glass or a plastic material. Generally, in order to bond a semiconductor wafer incorporating the devices to a protective wafer a bonding material is used, such as, for example, a glass frit. More precisely, the bonding material is deposited in purposely provided areas of the semiconductor wafer or, more frequently, of the protective wafer, so as not to interfere with the devices incorporated. The two wafers are then bonded and kept pressed until the bonding material expands and adheres to both of them.
Conventional bonding techniques present, however, limits, especially in the case where microelectromechanical devices are provided. In this case, in fact, the surface which is to be bonded is limited by the overall dimensions of the devices, and the adhesion of the bonding material is not always sufficient to guarantee sealing thereof. In general, adhesion of the bonding layer with a semiconductor material is not sufficiently strong and there is a considerable risk of delamination, which occurs more frequently on the side of the device. In other words, when the composite wafer is cut or following upon stresses during use, the semiconductor wafer or a portion thereof containing a device tends to detach from the corresponding cap.
The risk of delamination is higher on the side of the device, which normally requires a more complex machining and for this reason presents surface irregularities and defects with greater frequency.
In the case of delamination, the device (if not the entire wafer) is in practice unusable and must be rejected.